Devices that increase the stability of a vehicle while driving include an Anti-lock Brake System (ABS) for preventing slippage upon braking, and a Traction Control System (TCS) for preventing slippage upon sudden acceleration.
In addition, Electronic Stability Programs (ESPs), which assist a vehicle in stably maintaining the attitude of the vehicle during driving so as to increase the driving stability of the vehicle, are currently being developed and used.
That is, the ABS is a system for ensuring braking stability, the TCS is a system for ensuring acceleration stability, and the ESP is a system for stably maintaining the attitude of the vehicle while controlling the torque of an engine or controlling a brake in cooperation with the ABS when the vehicle assumes a dangerous attitude.
The aforementioned systems for improving driving stability need to decide, for example, the longitudinal velocity and lateral velocity of the vehicle and road conditions using a plurality of sensors, such as a wheel speed sensor, a brake pressure sensor, a steering angle sensor, a yaw rate sensor, and a lateral acceleration sensor, and to control various restraint devices based on the results, in order to ensure the safety of the vehicle.
However, conventional systems for improving driving stability have derived desired values via the measurement of a wheel speed in the case of estimating the longitudinal velocity of the vehicle. Because tires are separated from the ground surface in the state where rollover of the vehicle occurs, the measurement error of the wheel speed increases, which makes it difficult to accurately measure the longitudinal velocity of the vehicle.
In addition, although the conventional systems have derived desired values using only a yaw rate and a steering angle in the case of estimating the lateral velocity of the vehicle, the estimation of the actual direction in which the vehicle travels has been impossible due to slippage of the vehicle in the situation in which rollover of the vehicle occurs.
Therefore, there is a demand for a system capable of accurately estimating the longitudinal velocity and lateral velocity of a vehicle even in a vehicle rollover situation, thereby ensuring the appropriate deployment of vehicle restraint devices when the rollover situation is sensed.